Judo was around since the 1880's well before it was in the Olympics so it'd be good to see a reference for some of those statements. Although atemi waza was out originally I have a video where Mifune demonstrates judo leg locks in the 1950s.

Leg locks were removed from shiai in 1916, I think, well before the Olympics, because of the injury rate, which is pretty much the same reason that they tend to be restricted to higher grades under many BJJ competition rulesets.

Randori is another matter, and they're still considered part of judo, but as most clubs train for competitive success and leg-locks aren't allowed in competition, they get neglected.

in judo class we learn the leglocks and illegal throws, but its make REALLY clear that these mean an instant disqualification in a competition

also, after doing kani basami and drilling it, i cant see how its that dangerous. i mean its a heavy fall but its no worse than many others we do constantly
the leglocks seem basically identical to what we get taught in bjj, same thing with small variations here and there

and yes, to answer the question again
competition judo rules are teh major suck at times

Roly,
Kani basami is not that dangerous. Except when someone refuses to peform ukemi from it, expecially heavyweights. And people do stupid things in shiai. So its quite dangerous if you lean forward into it so as to not be thrown on to your back.

The most direct reason its banned is Sumio Endo broke Yamashita's leg with it in 1980, but that was Yamashita's fault!